As Davnes007 explained, when you get rid of grain, you get rid of a bunch of small details in the picture that existed with it. DNR can become very noticeable. Go to Blu-ray.com and see how they feel about DNR.

The tint on the DVDs seems to me like it's coming from the source material. A bunch of 70mm scans came up once and they all matched the coloring of the DVDs. The Tantive walls were blue, the Death Star was green. It just seems like a lack of color correction on the part of Lucasfilm.